When a system such as a press machine, a machine tool, a construction machine, a ship, an aircraft, an unmanned conveying unit, an unmanned warehouse are central-controlled, a number of sensors for detecting the operative state of each section of the system and a number of actuators for controlling the state of the respective sections are required. For example, in the case of a press machine, the number of sensors and actuators exceeds 3000. For some systems, the number of sensors and actuators is greater.
As a central control system for central-controlling the aforementioned types of systems, it has been proposed a structure wherein a plurality of nodes are serially connected to each other, one or a plurality of sensors and actuators are connected to each node, and the respective nodes are successively connected to each other in the loop-shaped configurations via a main controller so that each node is controlled in response to a signal from the main controller.
In the case of the structure wherein the respective nodes are serially connected to each other in the above-described manner, there arises a problem as to how simultaneity of output from each node and simultaneity of control of each actuator are to be achieved. For example, in a structure wherein an address is allocated to each node and the node is controlled based on the allocated address, time delay attributable to the addressing process becomes a problem. For this reason, with respect to collection of outputs from the respective sensors and control of the respective actuators, satisfactory simultaneity cannot be achieved with the conventional structure.
Under such circumstances, the inventors abandoned technical concept of allocating an address to each node while employing a structure of serially-connected nodes, and proposed a serial controller in which each node is identified based on the order of connection of the respective nodes. In the serial controller of this type, since addressing process becomes unnecessary, time delay attributable to the addressing process is eliminated and a structure of the node is simplified.
The serial controller of this type is constructed as illustrated in FIG 4.
The serial controller is intended to be applied to a central control system for a press, and includes a host controller 200 adapted to totally control respective sections in the press. The serial controller further includes a main controller 100 which controls receiving and delivering of data between the main controller 100 and a plurality of serially connected nodes 10-1 to 10-N.
A group of sensors 1-1, 1- 2 . . . 1-N are arranged in respective sections of the press so as to detect the operative state of the respective sections of the press. Similarly, a group of actuators 2-1, 2-2 . . . 2-N are arranged in respective sections of the press so as to drive the respective sections of the press. The group of sensors 1-N and the group of actuators 2-N are connected to the node 10-N (N=1 to N). The nodes t0-1 to 10-N and the main controller 100 are serially connected to each other in a loop configuration.
FIG. 5 diagrammatically illustrates a frame structure of data frame signals usable in the central control system in case that the number N of nodes is five. These data frame signals are delivered from the main controller 100. After passing through the nodes 10-1 . . . 10-N, the signals return to the main controller 100. Incidentally, FIG. 5(a) shows a data frame signal generated immediately after it is outputted from the main controller 100, FIGS. 5(b), (c), (d) and (e) show data frame signals which are outputted from the nodes 10-1, 10-2, 10-3 and 10-4, and FIG. 5 (f) shows a data frame signal which is outputted from the node 10-5 (In the case of N=5, a signal which is fedback into the main controller 100).
The components of the data frame signal having a frame, structure as shown in FIG. 5 are as follows.
STI: first start code indicating the head position of an input data (sensor data) DI PA1 DI: input data (sensor data) PA1 DIq: input data from a sensor connected to the qth node PA1 STO: second start code indicating the head position of an output data (actuator driving data) PA1 DO: output data (actuator driving data) PA1 DOq: output data to an actuator connected to the qth node PA1 SP: stop code indicating the end position of a data row PA1 CRC: code for CRC check PA1 ERR: code indicating the content and the position of error
As shown in FIGS. 5(b) to (f), in the nodes 10-1 to 10-N shown in FIG. 4, a detection data DIq of a sensor 1 connected to a node is added between a start code ST1 and a start code STO, and output data DOq to an actuator 2 connected to the node is taken out from behind the start code STO.
Therefore, in this system, when the main controller 100 sends a data frame signal containing an actuator control data DO as shown in FIG. 5(a) to the node 10-1, the data frame signal is successively transmitted to the node 10-1, the node 10-2, the node 10-3, the node 10-4 and to the node 10-5. Thus, the actuator control data DO in the data frame signal is distributed to a corresponding node and detection data obtained from the group of sensors at the respective nodes are taken into the data frame signal. As a result, by the time the data frame signal returns to the main controller 100, all the actuator control data D0 are taken out as shown in FIG. 5(f), and the detection data of the group of sensors are taken into the data frame signal.
In this manner, with the device of the present invention, the CRC code is contained in the data frame signal so as to detect a communication error among the nodes and between the node and main controller in the nodes and the main controller. In addition, the error code ERR is contained in the data frame signal so as to detect the disconnection of a signal line between nodes as well as errors in the node. The content of the error is carried by the error code ERR and is delivered.
According to the conventional error detecting system, however, in case that an error occurs in such a manner that the detection data changes from "0" to "1" or "1" to "0" due to noise in the signal line between a node and a group of sensors or noise in the sensor itself, there arises a problem that it cannot be judged whether the change is a true data variation or data variation attributable to an error.
Especially, in an industrial environment for a press, a machine tool, a construction machine, a ship, an aircraft, an unmanned conveying unit, an unmanned warehouse or the like to which the serial control device is applied, noises are likely taken into the system. Accordingly, demand for adequate countermeasures for solving the aforementioned problem have been raised from users.
The present invention has been made with the foregoing background in mind and its object is to provide a data input device for a serial control device capable of reliably detecting errors generated in the system including an error between the sensor and the node, and capable of preventing control error due to the error data.